Telephone exchange system



y 1933- l. H. HENRY 1,916,760

TELEPHONE EXCHANGE SYSTEM Filed Aug. 23, 1932 9 Sheets-Sheet 1 6 i t k N I) b k N u L5 Q) Q R E I 3 t 5 E Q Q 5 Q .2; a N Q i MARG/NAL l I INVEN TOR H. HENRY By 6 am ATTORNEY July 4, 1933. l. H. HENRY TELEPHONE EXCHANGE SYSTEM Filed Aug. 23, 1932 9 Sheets-Sheet 2 lNVENTOR H. HENRY A TTORNE Y July 4, 1933. l H. HENRY 1,916,760

TELEPHONE EXCHANGE SYSTEM Filed Aug. 23, 1932 9 hee s-Sheet 3 3/0 320 -Q-\ ,D-nh D-IM ,a --HD- HO- -o- FIG. 30 F/G. 38 3/2 305 305 309 307 307 30 303 EMHL INVENTOR H. HE NR) A TTORNE Y July 4, 1933.

I. H. HENRY TELEPHONE EXCHANGE SYSTEM Filed Aug. 2:5, 1932 9 Sheets-Sheet 4 //vv/v TOR H. HENRY ATTORNEY July 4,1933. 1. H. HENRY 1,916,750

TELEPHONE EXCHANGE SYS TEM Filed Aug. 23, 1952 9 Sheets-Sheet 5 lNVEN TOR H. HE NR) A TTORNE Y Filed Aug. 23, 1932 9 Sheets-Sheet 6 [NVENTOR H. HENRY m UP A TTORNEY July 4, 1933. I H. HENRY 1,916,760

TELEPHONE EXCHANGE SYSTEM Filed Aug. 22:5, 1952 i 9 Sheets-Sheet 7 INVENTOR H. HENRY 6? 6% A TTORNE V FIG. 7

July 4, 1933- H. HENRY 1,916,760

TELEPHONE EXCHANGE SYSTEM 7 Filed Aug. 23, 1932 9 Sheets-Sheet 8 INVENTOR H. HENRY ATTORNEY July 4, 1933. l. H. HENRY 1,916,760

TELEPHONE EXCHANGE SYSTEM Filed Aug. 23, 1932 9 Sheets-Sheet 9 INVENTOR H. HE NR) ATTORNEY N TEDsTA Patented July 4, f 1933 TESIPATENTI OFFICE.

ISRAEL H. nanny, or EAST ORANGE, new JERSEY, Assrenon. TO BELLTELEPHQNE nasoaarromns, INCORPORATEQOF new roman. Y., A conrona'rron on NEW YORK 'rnrnrnonn EXCHANGE SYSTEM ag neaubn filed au uaes, 1932. Serial No. esocos.

This invention relates to telephone exchange systems and more particularly to 1c1r cuits for enabling an operator to complete calls over step-by-step, switches.

nections vat far greater speed and thus establish more connections within a stated period ifprovisionis made to enable the operator. to write up the designations of" desired connections upon akeyset at her position. Such an arrangement has heretofore been disclosed forenabling toll operators to complete con nections over panel dial switchingequipment in the Patent No. 1,780,908 granted November 11, 1930, to XV. WV. Carpenter and R. E} Hersey.

In accordance with the present invention, provision is made whereby an operator may set step-by-step switches to complete local or toll connections under the control of a set of ten digit keys at her position. This is accomplished through the provision or" a sender which becomes associated with the outgoing trunk circuit taken for use bythe operator to complete the desired connection, which sender is arranged to record thedigits of the line designation keyed by the operator and. to transmit directive impulses to step-by-step switches accessible over the outgoing end of the trunk circuit.

In step-by-step exchange systems the switch trains for completing connections may comprise a Variable number of selector switches dependent upon the character of the call to be established. 'For the purpose of discriminating between classes of calls'the trunks outgoing from the operators position are divided into groups, four for example, each group being individual to a particular class of call. All. trunks haveaccess through a group of link circuitsto a group of senders.

-. The ;ob-- ject' of the invention is to provide improved Any trunk taken for use by the operator becomes automatically connected to an idle sender immediately after the operator plugs a cord circuit of her position into the trunk jack. In order that the sender may know what class-of call it is to control and therefore how many series of impulses it should transmlt to selector switches, provision is made in the trunk circuit for setting up in the sender a class record corresponding to the group or class to which the particular trunk belongs. For this purpose each trunk,

depending upon thegroup to which it belongs, establishes class registration circuits trom the trunk to the sender as soon'as the sender becomes. connected to the trunk, over a tour control conductors, two of which are later used for transmitting digit registration control impulses from the operatorskeyset and two of which later form the impulsing loop from the sender to the selectors to be set thereby.

Four class records are thereby set up in the sender corresponding to the four groups of outgoing-trunks; These classes may be fixed, where all connections to be established by the sender will require the transmission of the same number of impulse series, or may be variable, where some connections made over the group of trunks may require a difierent number of impulse-series than otherconnections I over the same group. The grouping of the trunks and the corresponding class record established in the sender may also indicate plied from the sender or whether a difl'erent timing interval is required between successive series of impulses transmitted from the,

the sender begins to'transmit impulses in accordance with any registered digit as soon as the digit is registered. For var able class calls the sender may begin to transmit 1mpulses in accordance with any registered digit as soon as thedigit is registered or, if

whether or notimmediate ringing is to be ap- 8 desired, may delay the sending of impulses for a certain registered digit or digits until a succeeding digit has been registered or until the operator has keyed the start indication. 'lhis feature has been made the subect matter of an application 01"- I. H. Henry and it. E. Hersey Serial No. 630,010, filed herewith.

Forcontrolling the transmission of im- ')ulses from the sender to selector s itches, two polarised relays are provided, the timing of whose operation is controlled through the charging and dischr-irging of a condenser whereby timed impulses of a character which IZGS accur e setting of the selectors is at- The number of impulses of anyim-- ries transmitted is controlled by a group of sev i1 pairs of counting relays which are operated in succession by the impulsing relays, the number of pairs of relays operated during the transmission of any impulse series being under the control of the regis ter upon which the operatorhas registered that particular digit. The counting-relays are also employed in conjunction with the impulsing relays for measuring off time intervals between successive digit series to allow time for selectors to hunt for idle trunks and are also employed for measuring off a.

time interval for the application of ringing current irom thesender on such class calls require immediate ringingfrom the sender.

The time interval measured between successive digits for variable class calls may be varied by changing the number ofpairs of counting relays which will be operated in accordance with the class of call registration recorded in the sender. This featurehas been made the subject matter of the copending application of I. H.1lenry and R. E. Hersey above referred to.

For a more complete understanding of this invention, reference may be had to the following detailed description taken in connection with the attached drawings in which:

F 1 shows an operators cord circuit for extending connections to trunks, extending to dial switching o'l'iices and a portion or". the equipment at the operators position;

Fig. 2 shows the operators keyset and telephone set circuits;

Fig. 3 shows a trunk circuit. of one group or class terminating in jack accessible to the operators cord circuit of Fig. 1, and in a lir t selector switch and the diagrammatic re n-esentation of other selector switches and a called subscribers line;

Figs. 3B, 3C and 3-1) show modified strapping necessary when the trunk circuit belongs to other groupsor classes;

Figs. 4t and 5 taken together show a link circuit torassociating a sender such as is disclosed in Figs. 6 to 9, inclusive, with the trunk circuit of Fig equipment of the sender, Fig. 8 disclosing the impulse counting relays andrelays of three of the senderregisters, and Fig. 9 showing relays of the remaining registers of the sender; and

Fig. 10 is a diagram showing the manner in which the several figures of the drawing should be assembled to disclose the complete embodiment of the invention.

he trunk finder 150 shown in Fig.4 may be of the well known Strowger type having both rotary and vertical stepping movements,

but being used, as a hunting switch it is also equipped with a vertical group commutator and commutator brush. equipped with additional brushes to allord additional points-of access to control conductors extending to trunk circuits. v

The sender finder 550 of Fig. 5'is of th well known step-by-step rotary type having no definite normal position and always remaining standing when idle on the terminals of the sender last used in extending a connection.

The selector switches discloseddiagrammatically in Fig. 3 may be of the Well known Strowger type responsive to directive impulses transmitted thereto from the sender, but are preferably of the type usually employed for establishing toll connections.

Completion of a' call from cmintercepting trunk In addition, it is plug 101 to battery through the winding of.

relay 102 and the winding of marginal relay 103 in series and to battery in parallel therewith through the non-inductive winding 104: I

of relay 103. At the same time, the trunk lamp (not shown) is extinguished. Relay 102 operates but relay108 does not operate over a high resistance ground connected to the sleeve of the trunkemployed for interestablishes a circuit for the supervisory lamp .105 extending from battery over the inner 0. in Fig. 4 the trunk finder contacts and winding of relay 110 to ground cepting service from connector multiples, and

at the lowerright normal contact of key 111.

Relay 110 locks in a circuit from battery at.

and plug 101, upper normal contact of key 11 1, upper left winding of repeating coil 113,

upper b'ack contact of relay 103, lower winding of'relay 108, lower back contact of relay 109, upper back contact of relay 137, resistance 138 to battery and from ground through the other winding of the back bridge relay of the connector over the rings of jack 100 and plug 101, lower normal contact of key 114-, lower left winding of repeating coil 113, inner lower back contact of relay 103, intermediate lower back contact of relay 109, lower back contact of relay 137 to battery through high resistance 139. Relay 108 does not operate in this circuit and due to the high resistance 139 the back bridge relay of the connector does not operate.

'- lVhen the operator throws her listening key 111 to the right'or talking position re.- lay 110 releases and a circuit is established from ground at the outer left back contact of relay 201, conductor 112, upper right contact of key 111 to battery through the winding'of relay 117 which operates and establishes a circuit from battery at the inner contact of relay 102, inner lower contact of relay 117, conductor 115, to ground through the winding of relay 202. and connects battery over its outer contact, winding of relay 203, resistance 20 1, right back contact...of relay'201, conductor 205,

middle lower contact of relay 117, resistance. 119, middle lower back contact of relay 109,

inner lower back contact of relay 103, lower left winding of repeating coil 113, lower normal contact of key 114, rings of plug 101 and jack 100 to the trunk circuit. Ringing current or silent interval battery. operates relay 209 or relay 203, which connect ground through interrupter contacts 206, contact of relay 209 or relay 203, back contact of relay 207 to battery through the winding'of relay 208. Relay 208 operates and locks through the winding of relav- 207,:outer contact of relay 208 to ground at the inner contact of relay 202. lVith relay 208 operated direct ground is connected through resistance 20 1 to the ring of the trunk over the path traced for tripping ringing current and for holding relay 203 operated. Vhen the interrupter contacts 206 again open, relay 207 operates in the locking circuit of relay 208 and both relays are then held. operated to ground at the inner contact of relay .202. Vhen the interrupter contacts again close with relay 207 operated, relay 201 operates in a circuit Relay 202 operates froml'battery through its winding, front contact of relay 207, front contactof relay-203 to ground at interruptercontacts 206. Relay 201 locks over its right front contact to ground at the inner contact of relay 202,

opens the ringing circuit from the ring of the trunk through resistance 204 and the windings of relays "203 and 209, closes an obvious circuit through the upper winding of relay 200 and removes direct ground from the operating circuit of relay 117 in the cord circuit. Relay 117 is now held operated over the previously traced circuit to ground through resistance 210. 'Relay 117 of another" cord circuit of the position will not Had the cordcircuit been connected to an intercepting trunk circuit from a selector multiple, not requiring the trippingof machine. ringing, relay 201 would be operated over conductor 118, inner upper contact of relay 117 to ground at the contact of relay 103 which in this case will beoperated in ries with relay 102. Relay 201 upon operating will cause'the operation of relay 200.

' WVith relay'200 operated, atalking path is'estabished from the upper right-winding of repeating coil 113, inner upper right contact of key 111, conductor 120, upper contact of relay 200, right winding of repeating coil 211, condenser 212, lowercontact of relay 200,.conductor 121, innerlower right contact of key 111,to-the lower right windingof repeating coil 113. Assuming that the operators telephone'set 213 plugged up, the talking path just traced is inductively associated therewith through the left winding of repeating coil 211 and the operator is enabled to converse with. the calling subscriber to ascertain information concerning the deslred connection.

It will be assumed that the desired connection is of a character which can be completed over a trunk such as is shown in Fig. 3, with the straps 301, 302, 303 and 304connected as shown to, joint conductors 305 and 306, 307 and 308, 309 and 311, and 312 and 313, and with straps 325,326 and 327 also connected. The operator first tests for an idle trunk of the group by touching the tip of plug 122 to the sleeve of the "jack of a trunk of 'that group. If the trunk is busy there will be battery potential on the sleeve and this potential will be transmitted over the tip of plug 122, the upper normal contacts of relay 123, the upper back contact of relay 124, the

upper normal contact of key 125, conductor.

126, condenser 214:,to1gr0 und through the which induces the busy potential through the left winding of coil 215 into the operators telephone set 213 thus producing a click in her receiver. Assuming that she tests the trunk circuit of Fig. 3 and finds that it is idle and receives no click, she inserts plug 122 into jack 314 thereby establishing a circuit extending from ground through the windings of relay 315, sleeves of jack 314 and plug 122, windings of relay 127 and marginal relay 128 in series to battery and in paralwhich operates, opening the busy test circuit at its upper back contact and at its inner upper and inner lower front contacts, connects the tip and ring contacts of plug 122 to the right windings of repeating coil'113. Relay 127 at its lower contact also establishes a circuit for lamp 130 extending over the upper back contact of relay 131. Preparatory to keying the digits necessary to complete the connection the operator now depresses the key 216 and with the talking key 111 operated to the right a circuit is established from ground at the lower back contact of relay 218, the right contact or key 216, conductor 217, the lower intermediate contacts of key 111, the upper. winding of relay 123 to battery at the ower contact of relay 124. Relay 123 thereupon operates and locks in a circuit frombattery over the lowercontact of relay 124, lower winding and inner front contact of relay 123, conductor 132., back contact of relay 219 and in parallel to ground through resistance 220 and the winding of relay 218. Relay 218 operates in this circuit opening the initial operating circuit of relay 123 and closing an obvious circuit for relay 221 which operates. Relay 123 at its upper and lower alternate contacts disconnects the tip and ring contacts of plug 122 from the right windings of repeating coil 113 andconnects these contacts over conductors 133'and 134 with the operators keyset c1rcu1t'. 1

Relay 2-21 upon operatlng closes an obvious circuit to light lamp 222, connects ground 'over conductor 223 for supplying operating 1 ground tothe keys of keyset 224 and establishes a circuit from ground at its upper contact, through the windin g and upper normal contacts of rela 225 conductor 133 u ner alternate contacts of relay 123, tips of plug 122 and jack 314, lower back contact of relay 316,'upper front contact of relay 315, lower vwinding of relay 502. V

back contact of relay 317 to battery through the winding of relay 318. Relay 318 operates in this circuit but relay 225 being marginal does not receive .suiiicient current tof'op'erate at this time due to the high resistanceof relay 318.

Starting (012 11 77 circuit to hunt for the 86 Zcczfcd trunk level in which the selected trunk appears, in

the case assumed, the first or lowermost segment, and estabhshes a clrcuit from ground at the back contact of relay 401, overthe lowor contact of relay 400, the lower normal contacts of make-busy jack 402, conductor .403, the lowermost back contact of relay 500,

to batery through the winding of relay 501. Relay 501 energizes in this circuit and establishes a circuit for relay 502 extending from ground over the lower front contacts T of relay 501, the inner lower back contact of relay 503, conductor 504, back contacts of vertical magnet 404 and rotary magnet. 405, 7

conductor 505 to battery through the upper With relay 502 operated a circuit is now established for the-vertical magnet 404 of the trunk finder 450 which-may be traced from battery through the winding of magnet 404,

conductor 506, the lower back contact'of relay 507, contact or relay 502 to ground at the inner upper back contact of relay 500. Magnet 404 upon operating opens atits back" contact the circuit of relay 502 whereupon relay 502 in turn deener jizes, opening the cir cuit of magnet 404. Thus magnet 404 and relay 502 reciprocally control each other to cause the magnet 404 to step the brushes of fin e 450 vertically step by step until the commutator brush 406 engages the grounded segment 407; hen this occurs a circuit is established for relay 507 extending from ground on segment 407, brush 406, conductor 408, the uppermostback contact of relay 500, the upper Winding of relay507, conductor 508, the back contact of rotary magnet 405, conductor 505 to battery through the upper winding of relay 502. Relays 502 and 50'? operate in this circuit, relay 507 looking over its lower winding and inner lower front contact, inner lower back contact of relay 500, conductor 509 to ground at the lower alternate contacts of vertical oil'- ing through the upper winding of relay 502 whereupon relay 502 deenergizes in turn opening the circult of magnet 405/ Thus magnet 405 and relay 502 reciprocally con-.

trol each other to cause magnet 405 to'step 1 the brushes of finder 450 over the terminals of the first bank level to which they were previously raised until-the set of terminals,

is reached in the level to which the selected 1 trunk is connected. T hereupon a circuit is established from battery through the winding of trunk relay 321, the right contact of relay 318, the left normal contacts of relay 322, inner lower contact of relay 315, conductor 323, bank terminal 410, brush 411, conductor 412, upper front contact of relay 501, winding of relay 511 to ground through the lower winding of relay 502. Relays 321, 502 and 511 operate in this circuit, relay 511 closing an obvious circuit for relay 503 and a locking circuit for relay 501 extending from battery through thewinding and inner lower front contact of relay 501, the lower contact of relay 511 to 'ground at the intermediate lower norinal contacts of relay 1512 for holding relay 501 operated after relay 500 operates as later described, Relay 503 upon operating closes at its innermost upper contact a shunt around the lower winding of relay 502, causing the release of relay 502, closes at its lower front contact an obvious operating circuit through the upper winding of relay 500 and at its lower intermediate contact prepares a circuit for relay, 512. Relay 500 upon operating locks from off-normal ground on conductor. 509 over its innermost lower front contact and lower winding, conv duct-or 513 to battery at the back contact of relay 413and at its uppermost back contact and innermost lower back contact opens the initial operating and locking circuits of relay 507. Relay 507 thereupon releases.

At the trunk circuit upon the operation of relay 321, acircuit is established for relay 317 extendingfrom battery, winding of relay 317, inner fr'ont contact of relay 321 to ground at the inner upper front contact of relay 315. Relay 317 looks directly to ground at the inner upper front contact of relay 315 over its inner upper front contact and opens thecircuit of relay318 which upon deenergizing disconnects ground from start conductor 319 and opens the operating circuit of relay 321. Relay 321 is, however, held operated over conductor 323, inner lower front contact of relay 315, left normal con- 3,

tacts of relay 322 and the lower front contact of relay 321. When ground is removed from start conductor 319 group relay 400 releases if there is at the time no other trunk in the same group in a. selective condition.

H'zmtz'ng for an. idle sender 7 At the time relay 501 operated immediately following the starting of the link circuit, acircult was also establlshed for relay, 514

extending from battery through the winding of relay 514, overthe lower back contact'of test relay 515 to ground at thelower front contact of relay 501. At its upper front con tact relay 514 establishes a saturating circuit for the test relay 515 which may be traced from battery through the lower winding of rel-ay515, front contact of relay 514, through the middle winding of relay 515 to ground lay 515 does not, however, become energized sufficiently to attract its armatures. t its lower contact, relay 514 establishes a circuit for stepping relay 516 of the sender finder 550 which extends from battery through the winding of. relay 516, back contact; of stepnects the winding of the stepping magnet 517 H to ground at the upper back contact of relay 515 whereuponmagnet 517 energizes opening the energizing circuit of stepping relay 516. Magnets 517 and 516 thus reciprocally control each other thereby advancing the brushes of the sender finder 550 step by step in search of an idlesender. As soon as a terminal set is reached to which an idle sender is connected, a circuit becomes established for test relay 515' extending from ground through the middle winding of test relay 515, the upper front contact ofrelay 514, the lowermost back contact of relay 512, the upper winding of relay 515, the innermost upper front contact of relay 501, brush 518, con ductor 519, inner right back contact of relay 600, inner left back: contact of relay 601 to battery through resistance 602. Relay 515 now receiving current through all of its windings operates quickly locking ina circuit extending from ground over its upper front cont-act and upper winding, thence as traced to battery at the back contact of relay 601, opening at its upper back contact the operating circuits of relay 516 and magnet at the lower front contact of relay 501. Re- 9 i pleted its operation and relay 503 has oper contact of relay 514, the lower front contact of relay 515 to ground at the lower front con-- tact of relay 501. Relay 512 upon energizing closes a holding circuit for itself extending from battery through its winding, its innermost lower front contact to ground at the upper front contact of relay 503, opens at its intermediate lower back contact its own initial operating circuit, transfers the locking circuit of relay 501 from ground at the intermediate normal contacts of relay 512 to ground through the upper back contact of relay 514, the lower front contact of relay 515 and the lower front contact of relay 501, connects brushes 414 to 417, inclusive, of finder 450 to brushes 520 to 523, inclusive, of sender finder 550, establishes a circuit extending in parallel through the windings of relays 524 and 525 over the upper front contact of relay 512, brush 526, conductor 527, through the left and intermediate windings of relay 603, the upper normal contacts of relay 604, to ground at the. inner upper contact of relay 605 and at its next-to-upper con tact connects battery through high resistance 533, the back contact of relay 524, conductor 534, brush 423, conductor 424, through the winding'of relay 322 to battery for the purpose of marking the trunk busy so long as the link circuit is engaged therewith. Relays 525 and 603 operate in the circuit traced but relay 524 being marginal does not operate. At its upper contacts relay 525 bridges the upper contacts ofrelay 501 in the holding circuits of relays 511 and 321 to hold the latter relays operated following the release of relay 501 and at its lower contact-s estab lish'es an obvious circuit for relay 536 which closes an alternative holding circuit for re: lay 512 for holding relay 512 operated following the release of relay 503.

' Should asecond trunk of the same group be selected at this time with relay 500 op erated and relay 507 deenergized and the group relay 400 be operated, relay'400 will again mark the lowermost commutator terminal 407 as before but will now start the trunk finder normaly having first choice access to the group of trunks in the first level of its bank and in the tenth level of finder 450. This start circuit extends from ground at the back contact of relay 401 over the lower contact of relay 400, lower normal contacts of jack 402, conductor 403, the lowermost front contact'of relay 500, the innermost upper back contact of relay 507, conductor 528, the lower normal contacts of jack 418, thence through the relay of that link corresponding to relay 501. Since the commutator segments and bank multiples are slip multipled in the well known manner, the trunk finder started will step vertically to its tenth bank level when it will be arrested by its commutator brush corresponding to brush 406 engaging the tenth segment of its commutator which I ment is in accordance with the well known so-called paddle wheel start circuit arran gement. i

At the sender upon the operatlon of relay 603 an obvious circuit is closed for relay 606 which in turn closes an obvious circuit for relay 600. Relay 600 disconnects battery through resistance 602 to make the sender busy to other sender finders, connects ground over its outer left front contact to the start lead 607 extending to the sender time alarm circuit and connects the right winding of the sender time alarm relay 700 to the lead 608 and over its inner right front contact prepares a circuit for relay 609. Relay 606 also closes an operating circuit from ground at its inner lower front contact over conductor 610 to battery through the winding of relay 701 which operates closing ground to conductors 800, 801, 802, 900 and 901 for furnishing locking ground to the sender register relays and closing a circuit over conductor 702 to battery through the winding of relay 611. Relay. 611 operates to perform functions to be later described. Relay606 also closes an operating circuit for transfer relaysv803 and 804 in'series over conductor 811, outer right back contact of relay 703, conductor 704, to ground at the innerupper front contact of relay 606. v Relay 803 upon operating locks itself and relay 804 operated over its upper front contact, the upper back contact of relay 814, conductor 812, upper back contact ofrelay'612 to ground on conductor 704 and extends its locking ground over conductor 821, the right normal contacts and winding ofrelay 703 to battery.

Relay 703 operates and. looks over its right.

alternate contacts to v ground on conductor 704 and opens the initial operating circuit of relays 803 and 804. Relay 804upon operating connects the operating windings of the relays 805 to 808, inclusive, of the first sender register to the contacts of the key pulsing relays 705, 706, 7.15 and 716'in'readiness to register the first digit keyed by the operator.

Registering the class indication.

The trunks to which the sender has access are arrangedin groups-in accordancewith calls. Further subdivision ingrouping may be made as follows: trunks requiring automatic start of ringing and trunks not requiring automatic start of ringing;- trunks re uirinu 0.6 seconds timin between the transmission of series of impulses and trunks requiring 0.4 seconds timing between the transmission of seriesof impulses. Each group, consisting of trunks for which the sender is required to pulse out a single fixed numberof digits or of trunks for which the sender is required to pulse out several different numbers of digits under the control of the operators start key 226, and for which similar ringing and timing conditions are required constitute a class. The sender determines the class of the call at the time of seizure by the polarity of leads 306, 308, 311. and 313 of the truck to which it is connected.

The sender is arranged to function-with four classes oftrunks which will be hereinafter referred to classes A, B, C and D,

class relays 707 to 710, inclusive, being provided to register these classes. Any class may require a fixed number of digits to he keyed or a Variable number of digits followed by an operation of start key 226; automatic start of ringing or no ringing; 0.6 seconds timing between any" two series of impulses leading from each trunk circuit to the sender through the link circuit is determined by the arrangement of straps 301 to 304, inclusive.v With the sender now associated withv the trunk circuit the following relays of the sender may or may not be operated, dependent upon the strapping in the trunk circuit. If battery is connected to conductor 306, relay 613 operates in a circuit from conductor 306, brush 417 conductor 419, inner upper front contact of relay 512, brush- 523, conductor 537, inner upper back contact of relay 614, lower normalcontacts and wind ing of relay 613 to ground at the upper con-. tact of relay 606. If battery connected to conductor 308, relay 614 operates in a circuit from conductor 308, brush 416, conductor 420, neXt-to-inner-upper contact of relay 512, brush 522, conductor 529, upper back contact of relay 613, lowernormal contacts and winding of relay 614 to ground. atv the' v brush 415, conductor 432, contact 530 of relay-512, brush 521, conductor 531, lower back polarized relay 618, polarized relay 619 not receiving current in the proper direction to operate. Relay 618 in turn closes a circult from battery, winding of relay 615, lower back contact of relay 616, contact ofrelay 618 to ground on conductor 704. If battery is connected to conductor 313 and ground to conductor 311 current flows through the windings of polarized relays 618 and 619 in such direction as to operate relay 619 which in turn closes a circuit from battery,

winding of relay 616, low erback contact of relay 615, contacts of relay 619, to ground on conductor 704. Eitherrelay 613 or relay 614 upon operating looks from ground at contacts of relay 606 through its own winding and lower alternate contacts to battery through resistance 621. Either relay 615 or relay 616 upon operating locks from battery through its winding and upper front-contact to ground on conductor 7 04.

Relay 613 if operated connects conductor 306 over the path just traced to conductor 537, thence over the inner upper back contact of relay 614, lower front contact of relay 613, upper back contact of relay-612, conductor 623, windings of relays 716 and 724 to 24-volt battery, and c ductor 308 over the path just traced to conductor 529 thence over the inner upper front contact of relay 613, lower back cont-act of relay 612, conductor 622, windings of relays 705, 706 and 714 to24'yolt battery. Relay 614, if operated, connects conductor306 over the path traced to conductor 537, thence over the inner upper front contact of relay614,

lower back contact of relay 612, conductor 622, windings of relays 705, 706 and 714 to 24-Volt battery, and connects conductor 308 over the path traced to conductor 529 thence over the upper back contact ofrelay 613,

lowerfront contact of relay 614, upper back contact of relay 612, conductor 623,: Windings of relays 715, 716 and 724 to 24-volt ects con battery. Circuits for class relays 707 to .710,-

inclusive, are closed as follows: With relays 614 and 616 operated, class relay 707 is operated in a circuit from battery through its winding, conductor 713, inner upper front contactof relay 616 to ground at the upper front contact of relay 614; with relays 613 and 616 operated class relay 708 is operated in a circuit from battery through its winding, conductor 717, intermediate upper contact of relay 616, upper front contact of relay 613.to ground at the upper back contact of relay 614; with relays 614 and 615 operated class relay 709 is operated in a circuit from battery, through its Winding, conductor 718, inner upper front contact of relay 615,t0 ground at the upper front contact of relay 614; and with relays 613 and 615 opassociated trunk circuit to give the fourcl ass 1nd1cat1ons q Battery on Ground on Relays 0km Indication leads leads operated 308 and 313 306 and 311 614, 616, 707 306 and 313 308 and 311 613, 616, s 30s and 311 306 and 313 614, 615, 709 306 and 311 308 and 613, 615, 710

In the case assumed, the trunk of Fig. 3 1s a trunk of a fixed four-d1git class requlrmg the automatic start of ringing from the sender only in case the call is being completed by an inward toll operator and requiring a short interval of 0.4 seconds between the last two impulse series which are to be transmitted therefrom toset the connector switch and, consequently the straps 301 to 304 are connected as shown to connect lead 306 to lead 305 and thence over the lower back contact of relay 3' tips of jack 314 and plug 122, upper alt ate contacts of relay 123, conductor 133, upper normal contacts and winding of relay 225 to ground at the upper contact of relay 221; lead 308 tolead 307 thence over the upper back contact of relay 316, rings of ack 314 and plug 122, lower alternate contacts of relay 123, conductor 134, upper back cont-act of relay 227 to battery through resistance 228; lead 311 to lead 309 thence to ground through one winding of the control. relay not shown of the first selector 300 in which the trunk terminates; and lead 313 to lead 312, thence to battery through theother winding of the control relay of the first selector 300. Thus as indicated in the preceding'table, relays 614, 616 and class relay 707 are operated. As previously described relay 614 upon operating connects 24-volt battery through the windings of relays 705, 706 and 714 to conductor 306 and thence as traced to ground through the windingofrelay 225 at the operators keyset circuit, thereby operating relay 225 which locks over'its upper alternate contact through resistance 228 to battery, closes the circuit of relay'227 over its lower contact, the upper back contact of relay 229 to ground at the upper contact of relay 221 and closes the circuit of lamp 230 from battery througl'l the lamp, the lower back contact of relay 229,

its upper alternate and inner lower front contacts to conductors 134 and 133 and thence 7 over the circuits traced to, 24-volt battery through the windings of pulsing relays 715, 716 and 724 and the windings of pulsingrelays 7 05, 706 and 714, respectively.

Keying the called Zine designation It will be assumed that the operator in order to establish a connection to the line 360,

the designation of which is the four-digit number 1379, depresses the keys 235, 236, 237

and 238 in the order named. Upon the depression of key 235 to register the thousands digit 1 ground on conductor 223 is connected through lmvresistance 239, the contacts of key 235, conductor thence as traced to 24-volt, battery, tl'irough the windings of impulserelays 705, 706, and 714. Due to the inclusion of low resistance 239, su'l'licient cur rent flows to operate both the sensitive relay 714 and the marginal. relay 706, but polarized relay 705 does not receive current in the proper direction through its winding to cause its operation.

Relay 714 upon operating,with transfer relay 803 operated as previously described,

establishes a circuit extending from ground at its contact over conductor 822, inner lower front contact of relay 803, to battery through the winding of transfer relay 813. Relay 813 operates and locks in series with transfer relay 814 from battery through the windings of relays 813 and 814, middle upper front contact of relay 813, upper back contact of transfer relay 824- to ground on conductor 812, but relay 814 being shunted as long as relay 714 remains operated does not operate at this time. Relay 706, upon operating closes a circuit extending from ground at its contact over conductor 720, inner lowcontact of transfer relay 804, to battery through the lower winding of register relay 805. Relay 805 operates and locks over its upper winding and inner lower front contact to ground on conductor 800. e v

When the operator releases the depressed key 235, relays 706 and 714release, relay 714 removing the shuntfrorn around the winding of transfer relay 814, whereupon relay814 operates in the locking circuit of relay 813, opening at its upper back contact the locking circuit of transfer relays 803 and 804 whereupon these relays release. Relay 804 disconnects the operating circuits extending from the windingsof relays 805 to 808 inclusive of the first register from the contacts of impulse relays 7 05, 706,715, and 716, and relay 814 upon operating connects the contacts of the impulse relays to the windings of relays 815 to 818, inclusive, of the second register.

When the operator depresses key 236 to register the hundreds digit 3, 48-volt battery on conductor 232 through low resistance 231, is connected over the contacts of key 236, conductor 234, thence as traced'to 24-volt battery through the windings of impulse relays 7 05, 7 06, and 714. The direction of current now flowing through the windings of these relays is such as to operate the polarized relay 705 and since a low resistance has been included in the circuit relays 7 O6 and 714 also operate. Relay 714 upon operating with transfer relay 814 operated closes a circuit from ground over conductor 822, inner lower back contact of transfer relay 803, lower front contact of transfer relay 813, to' battery through the winding of transfer relay 823. Relay 823 operates and locksin series with the winding of relay 824, middle upper front contact of relay 823, conductor 831, upper back contact of transfer relay 904 toground on conductor 812, but relay 824 being shunted as long as relay 714 remains operated does not operate at this time. Relay 706 upon operating closes a circuit extending from ground at its contact over conductor 720, inner lower front contact of transfer relay 814, to battery through-the lower winding of register relay 815. Relay 815 upon operating locks over its upper winding and inner lower front contact to ground on conductor 801. Relay 705 upon operating closes a circuit extending from ground at its contact over conductor 721, lower contact of transfer relay 814 to battery through the upper winding of register relay 816. Relay 816 upon operating locks over its lower winding and front contact to ground on conductor 801.

When the operator releases depressed key 236, relays 705, 706 and 714 release, relay 714 opening the shunt around the winding of transfer relay 824, whereupon relay 824 operates in the locking circuit of relay 823, opening at its back contact the locking circuit of transfer relays 813 and 814 where upon these relays release. Relay 814 disconnects the operating circuits of register relays 815 to 8118 inclusive, from the contacts of im pulse relays 705, 7 06, 715 and 716 and relay 824 upon operating connects the contacts of these impulse relays to the windings of mg ister relays 825 to 828, inclusive;

When the operator depresses key 237 to register the tens digit 7 of the wanted line number, 48-volt battery on conductor 232 through low resistance 231 is connected through high resistance 240, left contacts of. key 237, conductor 234 thence as traced to 24-volt battery through the windings of impulse relays 705, 7 06 and 714. The direction of current now flowing through the windings of these relays is such as to operate polarized relay 705 and since high resistance 240 has been included in the operating circuit marginal relay 706 does not operate but sensitive relay 714 operates. Relay 714 upon operating with transfer relay 813 now released and transfer relay 823 operated, closes a circuit from ground at its contact over conductor 822, inner lower back contacts of relays 803 and 813, inner lower front contact of relay 823, conductor 832, winding of transfer relay 903 to battery. Relay 903 operates and locks in series with the winding of transfer relay 904, middle upper front contact of relay 903, back contact of transfer relay 914 to ground on conductor 812, but relay 904 being shunted as long as relay 714 remains operated does not operate at this time. Relay 705 upon operating closes a circuit extending from ground at its contact over conductor 721, lower contact of transfer relay 824 to battery through the upper winding ofregister relay 826. Relay 826 operates and looks over its lower winding and lower contact to ground on conductor 802.

Key 237 also closes a circuit from ground on conductor 223 through low resistance 241, right contacts of key 237, conductor 233 and thence as traced to 24-volt battery through the windings of impulse relays 15, 716 and 724. The current now flowing is'rnot in the proper direction to operate polarized relay 715 but since only low resistance 241 has been included in the operating circuit both relay 724 and marginal relay 716 operate. Relay 724 upon operating merely duplicates the function of relay 714 already described and relay 716 connects ground atits contact over conductor 722, upper front contact of transfer relay 824 to battery through the upper winding of register relay 828. Relay 828 operates and looks over its lower winding and lower contact to ground on conductor 802.

When the operator releases depressed key 237 impulse relays 7 O5, 714, 716 and 724 rd lease, relays 714 and 724 opening the shunt around the winding of transfer relay 904 which now operates in the locking circuit of relay 903 opening at its back contact the locking circuit of transfer relays 823 and 824 whereupon these latter relays release. Re-

lay 824' disconnects the operating circuits of the register relays 825 to 828, inclusive, from the contacts of the impulse relays. Relay 904 upon operating connects the contacts of the impulse relays to the windings of register relays 905 to- 908, inclusive. I

In response to the depression of key 238 for the units digit 9 48-v0lt battery is connected through low resistance 231 over conductor 232, the right contacts of key 238, conductor 233 and thence as traced through the windings of impulse relays 715, 716 and 724 to 24- volt battery. Due to the connection of 48- volt battery through a low resistance all. these impulse relays respond. Relay 724 upon operating connects ground at its contact over conductor 822, inner lower back con-- tacts of transfer relays 803, 813, and 823, conductor 833, inner lower front contact of transfer relay 903, conductor 911, inner left front conta ct of class relay 707 which was assumed to be operated, conduct-or 624 to battery through the winding of relay 625. Relay 625 operates and locks through the winding of relay 612, front contact of relay 625 to ground on conductor 704, but relay 612 being shunted as long as relay 724 remains operated does not operate at this time. operating closes a circuit extending from ground at its contact over conductor 722, upper front contactof transfer relay 904 to battery through the upper winding of re ister relay 908. Relay 908 operates and locks over its'lower winding and lower contact to ground on conductor 900. Relay 715 upon operating closes a circuit extending from ground at its contact over conductor 723, inner upper front contact of relay 904 to battery-through the upper winding of relay 907 and in parallel through the wind ing of relay 729 to battery. Relay 907 operates and looks over its lower winding and lower contact to ground on conductor 900. Relay 729 also operates but is ineflectiveat this time.

Key 238 also closes a circuit from ground through low resistance 239, high resistance 242, left contacts of key 238, conductor 234, thence as traced to 24-volt battery through the windings of impulse relays 7 05, 706 and 714 but due to the direction and strength of the current flowing only relay 714 operates duplicating the function of impulse relay 724 already described. v

When the operator releases the depressed key 238, impulse relays 714, 715, 716 and 724 release, relays 714 and 724 opening the shunt around the winding of relay 612, whereupon relay 612 operates in the locking circuit of relay 625, disconnecting ground from conductor 812 at its inner upper back contact thereby releasing transfer relays 903 and 904. Transfer relay 904 upon releasing dis connects the operating circuits of register relays 905 and 908, inclusive, from contacts of the impulse relays. Relay 612 upon operating disconnects the windings of impulse relays 705, 706 and 714 at its lower back contact from the impulse path previously traced to conductor 233 at the keyset circuit and extends the impulse path over its lower 1 front contact, conductor 626, right back con tact of relay 7 25, inner left back contact of Relay 716 upon relay 726 to 48-volt battery through the right winding of relay 727, and disconnects the windings of impulse relays 715, 716 and 724 at its upper back contact from the impulse path previously traced to conductor 234 at the keyset circuit and extends this impulse path over its upper front contact, conductor 627, inner left back contact of relay 725, outer left back contact of relay 726 to 48- volt battery through the left winding of relay 728. v I

At the keyset conductor 233 extends through the winding of polarized relay 243 to 24-volt battery and conductor 234 extends through the winding of polarized relay 244 to 24-volt battery. Relays 243 and 244 both operate but relays 727 and 728 being mar inally wound do not operate at this time. l/Vith relays 243 and 244 both operated an obvious circuit is closed for relay 245 which looks to ground at the upper contact of relay 221 and connects ground over its upper contacts to conductor 234 whereby marginal relay 727 in the sender operates and locks in a circuit extending from battery through the winding of relay 726, left winding and contact of relay 727, to ground on conductor 704. Relay 726 upon operating disconnects the operating windings of relays 727 and 728 from the circuits previously traced through the windings of polarized re lays 243 and 244 at the keyset circuit, relay 243 now releasing but relay244 being held operated over the upper contacts of relay 245. Relay 243 upon releasing closes a circuit from ground at its back contact, lower contact of relay 245, winding of relay 219 to battery. Relay 219 operates and opens the circuit of relay 218 which upon releasing in turn releases relay 221. Relay 221 upon releasing in turn releases relays245, 244, 219, 225 and 227 and extinguishes lamps 222 and 230. Relay 221 upon releasing also releases relay 123 in the cord circuit. The operators keyset circuit is now in normal condition.

If the operator disregards the pilot lamp 230 and starts keying a designation before the sender is attached and relay 227 has been operated from the sender, a circuit will be closed for relay 229 from battery through its winding, inner lower back contact of relay 227, conductor 234 to ground on conductor 223 through contacts of any operated key of the keyset 224. Relay 229 upon operating locks overthe left contact of key 216, upper front contacts of relay 229 to ground at the 3 keyset for use the operator must press key 216 to relase relay 229. Transmission of impulse/s60 selector switches Returning tofa consideration of the sender it will be recalled that relay 611 operated when the sender was seized. Upon its operation a circuit was established for operating impulse generating relays 730 and 731 extending from ground at its inner upper front contact, conductors 628, 629 and 630, resistances 7 32 and 733, resistance 735 to battery and in parallel over the lower contacts of .jack 734, left windings of polarized relays 730 and 7 31, upper contacts of jack 734, resistance 736 to battery in preparation for impulsing, relays 7 30 and 731 both operating. At this time, the impulsing loopto the first selector previously traced through the windings of relays 618 and 619 is now closed at the sender through the contacts of relay 730 and back contacts of relay 711 in parallel until relay 711 operates at the end of the synchronizing impulse as will be described.

' Relay 611 also at its lower front contact switches the condenser 631 and resistance 632 across the impulsing conductors 531 and 538 extending from the sender to the first selector 300. At this time condenser 742 associated with the impulse generating relays 730 and 731 is also charged in a circuit extending fromground through condenser 742, upper normal contacts of jack 741, right windings of relays 7 30 and 7 31,1ower normal contacts of jack 741 to battery through resistance 736.

It will be assumed that the sender is arranged to start the transmission of the first series of impulses as soon as the first digit has been registered on calls of classes A and C having a fixed number of digits and to delay the transmission of the first series of impulses until after the first two digits have been registered on calls of'classes B and D having a variable number of digits. For this purpose, straps 651 to'663, inclusive, of Fig. 6 straps 862 to 865 of Fig. 8 and straps955 and956. ofFig. 9 are connected as shown. As soon as the first digit has been registered on the relays of groups 805 to 808, inclusive,

and transfer relay 803 has released as previously described, a circuit for transfer relay 809. is established extending from battery through the winding of relay 809, upper back contact of transfer relay-810, lower back contact of relay 803, straps 651 and 652, conductor 681, outer right back contact of relay 737, relay 737 not being energized since the class assumed is the fixed four-digit class, conductor 738, straps 653 and 654, conductor 835,

inner left front contact of relay 703, conductor 740, left back contact of relay 836, conductor 633, to ground at the inner lower front contact of relay 616.

Relay 809 upon operating looks through the upper winding of relay 810, lower front contact of relay 809, conductor 852, right back contact of counting relay 842, conductor 634 to ground at the middle lower front contact of relay 606, but relay 810 being shunted does not, operate at this time. Re-,

lay 809 upon operating closes a circuit from ground on conductor 630, inner lower front contact of relay 809, conductor 635, upper back contact of relay 636, back contact of relay 637, upper back contact of relay 638, inner lower back contact of relay 604, conductor 639, front contact of relay 731, upper contacts of jack 734, left windings of relays 731 and 730, lower contacts of jack 734, to battery through resistance 735 and in parallel with the left windings of relays 7 31 and 730 to battery through resistance 736. The current flowing through the left windings of relays 730 and 731 now decreases since the left windings of these relays are now connected in a circuit from ground on conductor 630, through resistances 732 and 733 to ground and condenser 742 which was normally charged now discharges to ground on conductor 630, creatinga flux in the cores of relays 731 and 730 which gradually builds up as the condenser 742 approaches full dis charge in opposition tothe flux created by the left windings of these relays until a point is reached when the relays 730. and 731 both release differentially.

WVhen relay 731 opens its front contact the charging path for condenser 7 42 through the right windings of relays 730 and 731 previously traced is again effective, current now flowing through the right windings in the reverse direction and these relays continuing to release and to remain normal until condenser 742 approaches full charge condition and the current in the initial energizing circuit through the left windings of these re-' lays has reached operating strength, when relays 7 30 and 7 31 will again operate. This pulsing action continues until ground is removed from the armature of relay 7 31 by the release of transfer relay 809, following the transmission of impulses for the first digit, by the release of transfer relay 819, following the transmission of impulses for the second digit, by the release of transfer relay 829 following the transmission of impulses for the third digit, the release of transfer relay 909 following the transmission of impulses for'the fourth or last digit and the timing for trunk hunting between the transmission of digits has been allowed.

Upon the first release of relay 7 31 a circuit is established from ground on conductor 639, back contact of relay 7 31, conductor 743, right back contact of counting relay 836, right back contact of counting relay 838, back contact of counting relay 854, to battery through the winding of counting relay 853. Relay 853 upon operating locks through the winding of relay 854, front contact of relay 853, left back contact of relay 838 to ground on conductor 634, but relay 854 being shunted does not operate until relay 7 31 again operates. Relay 854 upon operating extends groundfrom conductor 634, over the left 

